Ok! That's interesting. I would have fed in the hard water not knowing.
Would it be possible/practical to leave the RO waste water in the plumbing system and let it go to my washer, dishwasher, shower etc? I'm not paying for the water, but it would still be pretty soft and seems like a waste to not use it. It might be ok to have the RO only switch on when someone in the house was using water anyway, and just let the RO water accumulate until there's enough for the next brew day.